1. Field of the Invention
The present invention relates to a method for providing a topically-resolved determination of the diffusion length of minority charge carriers in a semiconductor crystal body in which at least one electrolyte-filled measuring cell is applied to the semiconductor crystal body so that the front side of the body is in contact with the electrolyte, the semiconductor body is connected by way of an ohmic contact to a voltage source with which a voltage is applied between the semiconductor crystal body and an electrode located in the electrolyte, the front side of the semiconductor crystal body then being radiated with light from a light source, with which method defects and contaminants can be detected in a non-destructive manner.
2. Description of the Prior Art
Contaminants and defects in a semiconductor crystal body (generally and hereinafter referred to as a wafer) represent recombination centers for minority charge carriers. The diffusion length L of the minority charge carriers is therefore a measure for the density of defects in the wafer.
A method for the topically-resolved determination of the diffusion length L is disclosed in the European application 0 295 440. The front side and the rear side of the wafer are thereby each brought into contact with a respective electrolyte-filled measuring cell. An inhibiting space charge zone is generated at the rear side of the wafer with the assistance of a connected D.C. voltage source, the other pole of the voltage source being connected to an electrode located in the electrolyte of the measuring cell at the rear side. The front side of the wafer is irradiated with visible light of, for example, a helium-neon laser. The photo current of the generated minority charge carriers is detected at the rear side of the wafer and is normed to that measured at the front surface of the wafer. The diffusion length L is mathematically determined from this quotient.
The above method, however, can only be applied when the diffusion length L is greater than approximately 1/4th of the wafer thickness D since too few minority charge carriers otherwise diffuse up to the rear side of the wafer.